Two-stroke cycle internal combustion engine of the opposed piston type comprising two crank shafts



June 1958 J. E. JOHANSSON 2,84

TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINE OF THE OPPOSED PISTON TYPE COMPRISING TWO CRANK SHAFTS Filed Dec. 21. 1956 3 Sheets-Sheet 1 June 24, 1958 J. E. JOHANSSON 2,840,060

TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINE OF THE OPPOSED pxswon TYPE COMPRISING TWO CRANK SHAFTS Filed Dec. 21, 1956 :5 Sheets-Sheet 2 June 24, 1958 .JOHANSSON 2,840,060

TWO-STROKE CYCLE IN COMBUSTION ENGINE OF THE OPPOSED PISTON TYPE COMPRISING TWO CRANK SHAFTS Filed Dec. 21, 1956 3 Sheets-Sheet 5 scavenging-air ports and exhaust ferent pistons.

TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINE OF THE OPPOSED PISTON TYPE COM- PRISING TWO CRANK lolian Erik Johansson, Gotlienburg, Sweden, assignor t Aktiebolaget Gotaverken, Gothenburg, Sweden, a corporation of Sweden 7 Application December 21, 1956, Serial No. 629,818 Claims priority, application Sweden January 2, 1956 '1 Claim. ((31.123-41 This invention relates to two-stroke cycle internal combustion engines of the opposed piston type comprising two Qrankshafts and in which uncovering and covering of'the ports is controlled by dif- To improvethe performance of engines of the type indicated, there are several possibilities of timing the opening period of the exhaust ports relative to the open- 1 ing period of the scavenging-air ports. Prior to the uncovering of the scavenging-air ports,the' pressure in the .cylinder must be loweredto or below the scavenging 'air pressure, and for this reason it is absolutely'necessary that the exhaust ports be uncovered earlier than the scavenging-air ports. This may be achieved by increasing the axial extension of the exhaust ports as compared with the scavenging-air ports, which, however, results in the inconvenience that the exhaust ports will be covered later than the scavenging-air ports. .As a result thereof it is not possible to charge the engine up to the 'scavenging air pres- ;sure; There is also the possibility of having the cranks of the two, pistons movable in the cylinder angularly displaced relative each other in a manner such that the piston controlling the exhaust ports will lead by a few degrees of crank angle relative Ito the piston which controls the scavenging-airports. If the scavenging-air and exhaust ports are equally long, the exhaust ports will be uncovered earlier than the scavenging-air ports and will also be covered correspondingly earlier than the scavenging-air 'ports. By combining the lead in phase and an increased length of the exhaust ports the opening periods of the exhaust ports can'be timed in relation to the' opening periodsof the scavenging-air ports=in a manner such that all ofthe'ports will becovered at the same time, this being possible in a non-reversible engine. In a reversible engine, however, the exhaust ports must becover'ed later than the-scavenging-air ports so as to render possible the required earlier dischargeof the exhaust gases when the engine is running backward. In addition thereto, the uncovering of the exhaust ports. at forward rotation must take place. so early that even at the maximum engine output the pressurein the cylinder will be lowered to the scavenging-air pressure prior to the uncovering of the scavenging-air ports.

Theobject of the present invention is to improve engines designed as indicated above and is substantially characterized by the fact that one'or more resilient elements are comprised in the motion transmission means between the crankshafts such that upon increasing load onthe engine the lead in phase of the piston controlling the exhaust ports is increased relative to the pistonwhich controls the scavenging-air ports.

The invention is described more closely with reference to the annexed drawings in which Fig. l is a diagrammatic sectional view of a two-stroke cycle internal combustion engine of the opposed piston type having two crank shafts. Fig. 2 is a diagram representing the opening periods of the scavenging-air and exhaust ports. Figs. 3 and 4 illustrate diagrammatically the motion transmission means 2,840,060 Patented June 24, 1958 ICC between the crankshafts in unloaded and loaded condition, respectively, and Fig. 5 is a sectional view of a resilieut geanwheel forming part of the motion transmission means." i v I Referring to Fig. l, numeral 1 denotes a cylinder of a two-stroke cycle internal combustion engine which may .be of the multi-cylinde'r type. A lower piston 2 adapted to reciprocate'in' the cylinder is in the conventional manner connected with 'a crank 3 of a crankshaft by means of a connecting rod 4 and adapted to uncover and cover scavenging-airports 5. An upper piston 6 in the cylinder 1 is b'ynieansof a connecting'rod 7 connected to a crank 3 of an upper crankshaft and adapted to uncover and cover exhaust ports 9 the axial extension k of which is. greater than the axial' extension h of the scavenging-air ports 5. The two crankshafts are displaced relative each 1 other in a manner such that the upper crankshaft normally leads by an angle at relative'to the lower crankshaft, corresponding to a displacement k of the upper piston 6 relative to the lower piston in'the top dead centre thereof; The crankshafts are interconnected by means of a resilient gear transmission to be described later on. Although in the embodiment illustrated the lengths of stroke s of the pistons 2 and 6 are equal to each other, this need not necessarily be thejcase.

The ordinates of the diagram shown in Fig. 2 represent the'uncovered areas of the scavenging-air and exhaust ports asfunctions of different positions of the pistons, the origin of'the 'diagramrepresenting the bottom dead centre .of the piston 2. The distances from the origin to the left. of the axis of abscissae represent the positions of the respective pistons'ahead of the dead centre at forward rotation, for instance in terms of degrees of crank angle, whereas the distances to the right represent the corresponding positions after the dead centre. For backward rotation, the curves are to be read from the right to the left; uncovering'of the ports being shown at the right and covering of the ports at the leftof the axis of ordinates. The curve n represents the opening period of the scavenging-air ports 5, this curve being obviously symmetrical with respect-to the axis'of ordinates, the uncovered area of the exhaust ports'is greater than the axial extension of the scavenging-air ports. The combination of said increased axial extension and the lead in phase will sum up to the effect that the exhaust ports will be uncovered considerably earlier than the scavenging-air ports, whereas the lead in phase durin covering of the ports reduces the effect of the greater axial extension of the exhaust ports. The conditions may be chosen arbitrarily, for instance such as to have the exhaust ports and the scavenging-air ports covered simultaneously, as exemplified by the curve b. The fact that the exhaust ports are longer than the scavenging-air ports results in that the curve [2 lies above the curve 41, and the lead in phase results in that the top of the curve b is located ahead ofthe dead centre of the lower'piston 2.

If a resilient element is inserted into the motion transmission means between the crankshafts, the lead in phase will be increased as the load on theengine increases, so that the opening periodofthe exhaustports will be represented by the curve c from which it will be seen that the exhaust ports will be uncovered earlier than in the case of a non-resilient connection between the crankshafts according to curve 11, and it will be seen that the exhaust ports will be covered earlier too. Consequently, an engine having the combined features of lead in phase, longer be expected.

exhaust ports and resilient motion transmission. means will yield an increased output and will be able to be supercharged. ,1

As indicated, the above consideration applies to-thenormal direction of rotation of theengine. However, certain engines, such as marine engines directly connectedto the propeller shaft must bereversibl'e for astern propulsion. In an engine. according to the example described and merely having an increased length ofthe exhaust ports and a lead in phase, the'scavenging air ports and the exhaust ports would be uncoveredsirnultaneously as represented by the curves a and b. In this case the scavengingair pressure must be as high as the final compression pressure to prevent the exhaust gases from flowing back into the scavenging-air duct, this being not possible without the use of non-return valves or positively controlled valves in said duct. On the other hand, it is apparent from the above named curves that the exhaust ports would be covered considerably later than thescaVenging-air ports, resulting in a smaller charge. Even if such an engine could be reversed, it would be very uneconomical in operation and would yield a largely reduced output on direction [of rotation, the resiliency acts in the opposite direction andconsequently contributes towards a decrease of the lag of the upper piston relative to the lower one, said lag being a result of the leadupon forward rotation. In the diagram shown .in Fig. 2, the curve d' represents the courseof uncovering and covering of the exhaust ports at backward rotation, the uncovering and covering positions being reversed as comparedwith forward rotation. Consequently, the point of intersection with the axis of abscissae at the right of the axis of ordinates represents the beginning of uncovering which takes place earlier than the uncovering ofthe scavenging-air ports according to curve a. Consequently, the pressure in the cylinder wilt be lowered down mm below the scavenging-air pressure prior to the beginning of the scavenging.

On the other hand, the exhaust ports will be still open after the scavenging-air ports have. been covered, which means that supercharging at backward rotation can not In view thereof, the engine can not yield such a high continuous output at such a high efliciency as during forward rotation. However, in marine engines or the like, the time of backward rotation is usually so short that a temporary overload is permissible and a decrease in efficiency is of no consequence.

degrees of crank angle, while the resiliency in the tramh mission means will correspond to between :2 and :4

degrees of crank angle. i

As illustrated in Figs. 3 and 4, the transmission mechanism between the crankshafts is a gear transmission con sisting of a series of interengaging gears. Keyed onto the upper crankshaft 11 is a hub which by means of resilient spokes 12 is connected with a gear rim 13 the rotation of which is transmitted, by means of intermediate gears 14, 15, 16, to a gear rim 17 which by means of resilient spokes 18 is connected to the lower crankshaft 19 which is the single output shaft of the engine. When the engine is at rest, the gears are in the relative positions shown in Fig. 3. In operation, the resiliency of the spokes 12 of the gear wheel mounted on the upper crank shaft 11 results in an angular displacement between said, shaft and the gear rim 13, said angular displacement being transmitted, by means of the intermediate gears 14, 15, 16, to the gear rim 17 of the gear wheel on the lower crankshaft 19, the angular displacement being then, increased due to the resiliency of the spokes 18. The total angular displacement between the crankshafts 11 and 19 equals the sum of the angular displacements in the resilient gears.

During backward rotation, the resiliency will obviously act in the opposite direction from the neutral position such that the pre-adjusted;lead of the lower crankshaft will be decreased or entirely compensated for.

Fig. 5 illustrates a construction of a resilient gear wheel. The hub 21 is suitably secured to a journal of the crank shaft and has a plurality of circumfercntially spaced apart radial recesses 22 into which are inserted resilient spokes 23 which may consist of sets of leaf'springs. The outer ends of the spokes 23 are introduced into corresponding radial recesses 24 on the inside of a rim 25 having external teeth 26 which may be straight;or-helical. Between the spokes23 there are provided partitions 27 which are rigidly secured to the hub 2l and by means of sealing members 28 abut against the inner face of the gear rim 25. Separate chambers 29 thus formed on either side of each spoke 23 are variable in volume due to the resiliency of the spokes 23 such that the volume of one chamber is increased as the volume of the adjacent chamberis decreased. Through passages 30, the chambers 29 communicate with a source of oil under pressure to keep the entire gear wheel filled with oil which cools the gear wheel and serves as a shock-absorbing fiuid which passes from chambers being reduced in volume to the chambers with simultaneously increasing volume.

It will be understood that the invention is not limited to the described construction of the resilient transmission mechanism which may be modified within the scope of the appending claim.

What I claim is: V

A reversible two-stroke cycleinternal combustion'engine of the opposed piston type comprising twobrankshafts, a cylinder having exhaust ports and scavenging air ports, a first piston connected to one of said shafts and adapted to control said exhaust portions and a second pis- 7 ton connected to the other shaft and adapted to control said scavenging air ports, the axial extension of the exhaust ports from the bottom dead center of said first piston exceeding the corresponding extension of said scavenging ports, said first piston having such lead in phase relative to said second piston as to cause the exhaust ports during forward running and at low' engine load to be uncovered before and covered substantially simultaneously with the scavenging air ports, and motion transmission means interconnecting said two shafts and including at least one resilient member operative in both directions of rotation and adapted upon increasing load on the engine to increase the lead in phase of said first piston relative to said second piston, the resiliency being of such magnitude as to ensure uncovering of the exhaust ports before the scavenging ports during astern running of the engine.

ReferencesCited in the file of this patent UNITED STATES PATENTS Ford Nov. 23, 1943 

